TF-900_TM800

[sinclairuser]

hi ivica, those phone numbers starting 44, are all UK numbers, dont know about 49, though.

is this unit similar to that cscope unit made by discovery and discussed in an earlier thread?, the style of board and its production looks very early cscope, those solder tabs on the edges of the board can be seen on loads of old cscope units.
the discovery detectors must have been good units, if whites and cscope had them build units instead of rolling their own.

[ivconic]

No, completely wrong, I think.. Re-read my post.
Look at the photos of the TX board - see where the thick wires go. You have the power supply conected directly to a short circuit, ffs. And you have it reversed. It's a PNP bipolar transistor, the emitter goes to the +ve supply, the collector to the -ve supply.

Are there any other '6520' transistors on the main board ? That way you can find out if it's pnp or npn. Edit, yes there is, it's an MPS6520, which is npn, that's one problem solved.

Got to say, the two photos of the TX board show completely different wiring of the toroid. Confusing.

If you zoom a bit into this photo; you'll clearly see it is MPSA6520, NPN transistor.
I don't see any short circuit!??

[ivconic]

Actually... the way it is on last photo I posted; fat wire, red one, 75 turns, goes between Vcc and GND and in that case you are right, there is short circut (disregarding small 75 turns resistance).
But I posted this photo now, second ago, previously I think i did nothing wrong on drafts??
Damn this is confusing!
One thing is for sure; it is MPSA6520... unless somebody purposelly placed it there to make such photo!

[ivconic]

Thing is; I don't have TX pcb. I only have dozen photos downloaded from various topics in time.
So... sane logic confronts with what we see on last photo that i posted.
I am confused...
For the RX pcb I can asure you it is alright, because i checked it.

[ivconic]

hi ivica, those phone numbers starting 44, are all UK numbers, dont know about 49, though.

is this unit similar to that cscope unit made by discovery and discussed in an earlier thread?, the style of board and its production looks very early cscope, those solder tabs on the edges of the board can be seen on loads of old cscope units.
the discovery detectors must have been good units, if whites and cscope had them build units instead of rolling their own.

49 is from Germany.
I've been seeing less lately and the display on my phone isn't big.
And it happened that the phone rang and I answered immediately.
In the distance there is a rustling, sometimes a screaming female voice with a very bad accent ... "ivicha ... ivichaa", something like that.
And roaming is very expensive, it doesn't pay to fool around and talk to a stranger like that.
These are scams, telephone scams. We know that the EU + UK is now full of refugees, a bunch of unemployed "southerners" and "easterners".
Many of them are illiterate, prone to crime, easy money, reluctance and laziness.
I saw such people while I was in Malta, overnight they came to the shores of Malta in small boats and smuggled.
The next day you see them on the corners of the streets ... women are whoring for money, besieging passers-by and men are sitting idle all
day and just making up some petty criminal acts. The state is obliged to take care of them socially, as much as possible, so it gives them
a small amount on a weekly basis, just to survive.
I saw that back in 2004/5. in Malta, and now it is a harsh reality for the whole EU and the UK. And in a much larger number.
I follow the foreign media, I am up to date with the events. Black days are coming for all of us!
So the number of such phone calls and attempts of various scams has drastically increased in the last couple of years.
That is why I have blocked all foreign calls in advance and I am making a black list of all those who call.
...
The solder tabs on the edges are not just a Cscope feature, all the old detectors were mostly similar.
I had the opportunity to open dozens of ancient detectors and see similar or the same.
I know almost nothing about Discovery but I remember reading somewhere on the forum that someone (maybe Carl) wrote that the
TF900 and TM800 are the same machines and that the TM808 is drastically different. I have schematics so I can compare and I think that's true.

[Skippy]

MPS6520 from your main board photo: attached.

It's curious that only one winding is 'thick'. Obviously a feedback winding that coupled to the base of the transistor would only need to be thin.. but the second thin one?

[ivconic]

After you warned me that something was wrong there; I reviewed all the photos I have and really something is not right there !?
I guess some of the pictures were taken by someone who was messing around on a TX pcb and tying the wires wrong.
Either by accident ... or deliberately fooling others who watching. There are all kinds of them... the people.
So we don't need to take those photo for granted.
That is why I trust only and exclusively in my work, of this kind. Because I saw a lot of pranks of various pranksters.
That's why I did everything from the beginning on the main pcb. And that's why it is working right now. And I will solve this too.

[ivconic]

This is the only proper version, I think:



CBE pads are correct on pcb.
MPSA6520 is having EBC pinout and that's why it must be rotated, which is not on a drawing.
Not a problem as long as it not confusing the observer.
But here it is the way it should be:



On a photos however, MPSA is turned alright, rotated. That's the correct part.
Only the wires on the photos are soldered wrong.

[ivconic]

If my version is correct; than schematic will look like this:



I am still drawing it, not finished yet.

[Skippy]

It might be wise to add two pcb pads in parallel with the 33nF TX tuning capacitor, so a little more capacitance can be added, like on the RX board. Sure, small caps can always be tacked on the underside of the board.
Use one of the spare edge fingers as a second 0 Volts ground. And add a 100nF decoupling cap across the power rail. Maybe a tantalum / electrolytic cap too.

-----

I'm unsure what effect the single short-circuited turn of the main TX coil will have on tuning. It's going to add damping, but probably won't change the frequency much.

[ivconic]

It might be wise to add two pcb pads in parallel with the 33nF TX tuning capacitor, so a little more capacitance can be added, like on the RX board. Sure, small caps can be tacked on the underside of the board.

I'm unsure what effect the single short-circuited turn of the main TX coil will have on tuning. It's going to add damping, but probably won't change the frequency much.

Yes, a very interesting way of inductive coupling! And it makes sense, if you look at it as an ordinary transformer!
You have a bifilar center tapped ciruit that is "drive" and act as "primary", and you have an LC tank with thick wire and many more turns, acting as secondary.
Also preciselly tuned to RX with same thick wire and same number of turns.
An aluminum antenna passes through the toroid, acting as an elongated core, a special shape that "radiates" just like any antenna.
A coil with a thick wire, "secondary", in this case amplifies both the voltage and the current at a given frequency, because it has a larger number of turns,
it acts as a transformer that raises the voltage ...
And now as I write this and look at the schematic; at the same time I get a phenomenal idea, how to finally satisfy all those
tireless soil "shockers" who would want and like to drive a nail or similar into the soil and thus "emit frequency" (or whatever) into the soil ... I remembered a topic from before some day.


P.S.
Adding extra pads parallel to LC tank is alright, no harm. It may contribute in finest tuning.
RX ant TX both do have same 75 turns with the same wire. But never mind how precise you make those; it is impossible to make them exactly the same.
So, your suggestion is making sense to me.

[ivconic]

Now that we've elaborated on all this ... I conclude that it's smarter for me to take out the original RX board and remove the toroid from it and unwind
the wire and ... throw it away.
And then to find two 100% identical toroids and wind the same number of windings on them with the same wire.
Because if I leave the original RX toroid and start looking for a similar one ... the chances are slim that it will ever work properly.
Now, after this elaboration and correspondence, things are much clearer to me too! And so I will do, the original RX toroid goes in the trash!

Before that, I will just check the original resonance ... although it is also unnecessary, a simple LC calculator is an easier choice ...

[Skippy]

No .... keep the working circuit. Plus, the RX is simpler to change, it's just one simple inductor. You can make sure any clones with a new coil are correct by comparing their operation with the original one.
If you just want to experiment with the original, to find out its A_L value for example, you can just add extra windings, no need to remove any existing wire. Example wind exactly 50 Turns, measure L. As long as the original wire is not connected to anything, it's presence should be unimportant.

------

Don't forget the polarity of the two thin wires is important, so label one wire end with a black permanent marker/ paint, so you know start and finish. It won't oscillate if one winding is 'reversed'.

[ivconic]

No .... keep the working circuit. Plus, the RX is simpler to change, it's just one simple inductor. You can make sure any clones with a new coil are correct by comparing their operation with the original one.
If you just want to experiment with the original, to find out its A_L value for example, you can just add extra windings, no need to remove any existing wire. Example wind exactly 50 Turns, measure L. As long as the original wire is not connected to anything, it's presence should be unimportant.

------

Don't forget the polarity of the two thin wires is important, so label one wire end with a black permanent marker/ paint, so you know start and finish. It won't oscillate if one winding is 'reversed'.

[AK48]

hello , pics of C-SCOPE TF9000 HPX , same board but mine is populated and yours not, why ?